Method for producing phosphonium phenolates

ABSTRACT

A process for preparing phosphonium phenolate is disclosed. The process entails a reaction of phosphonium halide with phenol in an aqueous alkaline solution at a temperature of 0 to 55° C. The molar ratio of phenol to phosphonium halide is between 2:1 to 10:1 and the pH of the solution is 9.5 to 11. An optional embodiment entails carrying out the reaction in the further presence of alcohol.

This is the national phase of PCT/EP98/03590, filed Jun. 15, 1998, nowWO99/00395.

German application P 196 35 656.3 relates to a process for preparingphosphonium phenolates which is characterised in that phosphoniumhalides are reacted with phenols in a mixture of water, aqueous causticalkali solution and inert solvent for between 2 minutes and 4 hours attemperatures from 0° C. to 40° C. and at pressures from 1 bar to 20 barin the molar ratio 0.5 mol to 2 mol of phenol, preferably 0.7 to 1.3moles of phenol, per mole of phosphonium halide.

CH₂Cl₂ and C₆H₅Cl are mentioned as inert solvents in that document.

On page 4 of the German patent application P 196 35 656.3 it is alsoshown that phosphonium salts are converted into the correspondingphosphine oxide by bases. This is demonstrated in example A of thisapplication, wherein a pH of about 14 is used. (See also comparisonexample in this application and German application P 19723524.7, whichwas filed on May 6, 1997 with intermediate priority date over P19635656.3.)

During further development of this process it has now been found thatalcohols which are sparingly soluble in water, that is up to a maximumof 15 wt. % solubility, may be used instead of inert solvents.

It was also found, surprisingly, that the formation of phosphine oxidesis suppressed if the reaction is performed in alkaline solution, evenwithout an alcohol, at a pH between 9.5 and 11, preferably between 9.5and 10.5 and in particular between 10.0 and 10.5.

The present invention, therefore, provides a process for preparingphosphonium phenolates from phosphonium halides and phenols in aqueousalkaline solution at temperatures from 0 to 55° C., preferably 15 to 50°C., which is characterised in that the reaction is performed in themolar ratio of phenol to phosphonium halide between 2:1 and 10:1,preferably between 4.5:1 and 6:1 and in particular 5:1, at a pH of 9.5to 11, preferably 9.5 to 10.5 and in particular 10 to 10.5 andoptionally in the presence of alcohols in amounts of 50 wt. % to 200 wt.%, preferably 66 wt. % to 125 wt. %, with respect to the weight of theaqueous phase, wherein the alcohols have a solubility in pure water ofat most 15 wt. %.

Phosphonium phenolates can be prepared in high yields using the processaccording to the invention.

Phosphonium phenolates are suitable in particular as catalysts foresterification and transesterification, in particular to preparepolycarbonates by the melt transesterification process (see U.S. Pat.No. 3,442,854).

The solubility of alcohols in water is known from the literature.

Suitable alcohols according to the invention are aliphatic alcohols withthe formula C_(n)H_(2n+1)OH in which n is an integer from 3 to 10inclusive.

Suitable alcohols according to the invention are also cycloaliphaticalcohols with the formula C_(n)H_(2n−1)OH in which n is an integer from5 to 10 inclusive.

Preferred aliphatic alcohols are (iso)butanols, pentanols and hexanols,in particular isobutanol.

Preferred cycloaliphatic alcohols are cyclopentanol, cycloheptanol andcyclooctanol, in particular cyclohexanol.

The ratio by weight of water to alcohol is between 2:1 and 0.5:1,preferably between 1.5:1 and 0.8:1.

The sparingly soluble alcohols to be used according to the invention areadded to facilitate the working-up procedure, since the phenol/alcoholmixture has a lower density than the aqueous solution and thus theorganic phase is above the aqueous phase. The aqueous phase can thus bedrawn off from below. The organic phase which contains the phenolate canthen be washed with deionised water in the same separating vessel andthe wash water can again be drawn off from below.

If an alcohol is not added, then the salt-containing aqueous solution isthe only phase more dense than the organic phase and it can thus bedrawn off from below. During the subsequent wash procedures usingdeionised water there is a phase inversion, the organic phase is thenthe denser phase and therefore is found below the aqueous phase. Thisworking-up procedure has proven to be more costly in so far as a secondprocessing vessel is required.

Phosphonium halides of the formula (I) are particularly suitable for thereaction according to the invention

in which

R₁ to R₄ are identical or different, and each represents a C₁-C₁₂ alkyl,C₅-C₆ cycloalkyl, C₇-C₁₂ aralkyl or C₆-C₁₄ aryl group,

and

X⁽⁻⁾ represents a halide ion, preferably F⁽⁻⁾, Cl⁽⁻⁾ or Br⁽⁻⁾ and n is 1or 2, wherein n is 2 when R₄ represents a C₂-C₁₂ alkylene group.

The groups R₁ to R₄ are identical or different, and each, preferably,represents a C₆-C₁₄ aryl group or the groups R₁ to R₃ each represent aC₆-C₁₄ aryl group and R₄ represents a C₂-C₁₂ alkylene group.

These types of phosphonium halides and methods for their preparation areknown (see for example “Houben-Weyl, Methoden der organischen Chemie”volume XII/1, pages 79 et seq and Worrall, J. Amer. Chem. Soc, 52(1930), pages 293 et seq).

These compounds (I) are produced during the reaction of trialkyl ortriarylphosphines, for example triphenyl phosphine, with halogenatedaromatic compounds or halogenated alkyl compounds, e.g. benzyl bromide,in the presence of metal salts (Friedel-Crafts alkylation) or in thepresence of Grignard reagents and cobalt(II) chloride.

Preferred phenols are those of the formula (II)

in which

R₅ to R₇, independently of each other, represent H, C₁-C₁₂ alkyl, C₅-C₆cycloalkyl, C₇-C₁₂ arylalkyl and C₆-C₁₄ aryl groups; R₅ to R₇ arepreferably hydrogen atoms.

These types of phenols are known from the literature.

Preferred phosphonium phenolates are thus those of the formula (III)

in which the groups R₁ to R₇ correspond to those in formulae (I) and(II) and n is again 1 or 2.

Deionised water or distilled water is preferably used for preparing theaqueous alkaline phase.

The pH can be adjusted to 9.5 to 11.0, preferably 9.5 to 10.5, inparticular 10.0 to 10.5, using a caustic alkali solution, preferablycaustic soda solution or caustic potash solution, taking into accountthe buffering effect of phenol/Na phenolate.

The process according to the invention may be performed continuously orbatchwise, wherein a batchwise mode of operation is preferred.

According to a preferred mode of operation, phenol, phosphonium halideand alkanol as solution are initially introduced and water is thenadded. The pH is adjusted to 9.5 to 11.0, preferably 9.5 to 10.5, inparticular 10.0 to 10.5 by adding caustic alkali solution, optionallywith cooling. The temperature is maintained at 0 to 55° C., preferably15 to 50° C., preferably with vigorous mixing of the reactioncomponents. The reaction should be allowed to continue for a period ofup to 2 hours, preferably up to 1 hour.

The phosphonium phenolate prepared according to the invention ispreferably isolated, when using an alcohol which is sparingly soluble inwater, by separating the aqueous phase from the organic phase,extracting the organic phase at least once, preferably 3 times, withdeionised water or distilled water, then removing the alcohol, forexample by distillation, and drying the reaction product after removingthe phenol. If the phosphonium phenolate is produced in crystalline formduring the two-phase boundary reaction according to the invention, thesecrystals may be recovered using conventional working-up procedures,inter alia by washing with deionised water or distilled water,optionally after recrystallising and drying.

If a sparingly soluble alcohol is not used, the precipitated crystalsare extracted with deionised or distilled water.

Quaternary phosphonium phenols prepared according to the invention arein particular

Use of the phosphonium phenolates obtained according to the invention toprepare aromatic polycarbonates may take place in a manner known per se(see U.S. Pat. No. 3,442,854 loc cit).

As is well known the melt transesterification process uses, for example,aromatic diphenols, esters of diaryl carbonates and optionally branchingagents and/or monophenols as starting materials.

The phosphonium phenolates obtained according to the invention are usedin this process as catalysts in amounts of 10⁻¹ moles to 10⁻⁸ moles,preferably in amounts of 10⁻³ moles to 10⁻⁷ moles, per mole of diphenol.

Further details relating to the melt transesterification process aredescribed in the literature (see for example Hermann Schnell, Chemistryand Physics of Polycarbonates, Polymer Reviews, Vol 9, 1964, pages 44 to51, DE-A 1 031 512, U.S. Pat. Nos. 3,022,272, 5,340,905 and 5,399,659).

Thermoplastic polycarbonates prepared using phosphonium phenolatesobtained according to the invention are solvent-free, have anintrinsically pale colour and the final polycarbonate is largely free ofunwanted defects.

The polycarbonates prepared in this way may be used on an industrialscale in the form of a very wide variety of moulded articles, in allareas in which thermoplastic polycarbonates have been used hitherto, forinstance in electrical engineering components, as lamp covers, as safetyshields or as CD material.

EXAMPLES

Comparison example (see example A in P 19635656.3 and P 19723524.7)

88.0 g (1.0 mol) of phenol, 88.0 g (0.99 mol) of 45% strength causticsoda solution and 1.5 l of triply deionised water are initiallyintroduced into a 2.5 1 round-bottomed flask with a stirrer,thermometer, reflux condenser and dropping funnel and stirred at 20° C.to 25° C. The pH is about 14. 41.93 g (0.10 mol) oftetraphenylphosphonium bromide are added to this solution. The mixtureis then stirred for at least 0.5 hours. After phase separation, theorganic phase is washed 3 times with triply deionised water and thenevaporated down. The crystalline residue is dried at 100° C. undervacuum.

Example 1

470 g (5.0 mol) of phenol, 1.0 l of triply deionised water, 419.3 g (1mol) of tetraphenylphosphonium bromide and 800 g of isobutanol areinitially introduced into a 2.5 l round-bottomed flask with stirrer,thermometer and dropping funnel and stirred at 20° C. to 25° C. 106.7 g(1.2 mol) of 45% strength caustic soda solution are then added dropwiseover the course of 2 minutes. The pH is checked using a glass electrode;it should be within the range 9.5 to 11.0. The mixture is then stirredfor at least 0.5 hours at 45° C. After phase separation, the loweraqueous phase is drawn off and the organic phase is washed 3 times withtriply deionised water. The wash water, as the denser phase, can bedrawn from below each time. Then the isobutanol is distilled off at 50°C. under a water jet vacuum.

The crystalline residue is dried at 100° C. under vacuum. The yielddetermined by the P—NMR method is 98.2% of the theoretical yield.

Example 2

419.3 g (1 mol) of tetraphenylphosphonium bromide are dissolved in 940 g(10.0 mol) of phenol at 40 to 45° C. in a 5 l round-bottomed flask withstirrer, thermometer and dropping funnel, then 500 ml of triplydeionised water are added. 133.3 g (1.5 mol) of 45% strength causticsoda solution are added dropwise over the course of 2 minutes. The pH ischecked using a glass electrode; it should be within the range 9.5 to11.0. The mixture is then stirred for at least 0.5 hours at 40 to 45° C.After phase separation, the aqueous phase (lower phase) is removed andthe organic phase is washed 3 times with triply deionised water. A phaseinversion occurs, since the aqueous phase is now less dense than theorganic phase. The organic phase is drawn off and washed in a differentvessel with triply deionised water, this process is repeated 3 times. Aphenolic solution with 37% of tetraphenylphosphonium phenolate isobtained.

The yield determined by the P—NMR method is 100% of the theoreticalyield.

Application examples

B1) 114.15 g (0.500 mol) of bisphenol A and 113.54 g (0.530 mol) ofdiphenyl carbonate are weighed into a 500 ml 3-necked flask withstirrer, internal thermometer and Vigreux column (30 cm, with plates)with bridges. Atmospheric oxygen is removed from the apparatus byapplying a vacuum and flushing with nitrogen (3 times) and the mixtureis heated to 150° C. Then 0.0173 g (4×10⁻³ mol. %) oftetraphenylphosphonium phenolate (TPP—P) prepared in accordance withexample 1, with respect to the bisphenol A, is added as a 3% strengthphenolic solution and the phenol produced is distilled off at 100 mbar.At the same time the temperature is increased to 250° C. The pressure isthen decreased stepwise down to 1 mbar and the temperature is increasedto 260° C. Then the temperature is increased to 280° C. and the mixtureis stirred for 1.5 hours at 0.1 mbar. A pale coloured, solvent-freepolycarbonate with a relative solution viscosity of 1.250(dichloromethane, 25° C., 5 g/l) is obtained.

The concentration of branching agent of the formula (VII) in thepolycarbonate prepared is 25 ppm. The phenolic OH-value of thepolycarbonate is 70 ppm.

B2) As in example B1), except that the temperature is increased from260° C. to 300° C. and the mixture is stirred for 1.5 hours at 0. 1mbar. A pale coloured, solvent-free polycarbonate with a relativesolution viscosity of 1.300 (dichloromethane, 25° C., 5 g/l) isobtained. The concentration of branching agent of the formula (VII) inthe polycarbonate prepared is 18 ppm. The phenolic OH-value of thepolycarbonate is 55 ppm.

What is claimed is:
 1. A process for preparing phosphonium phenolatecomprising a reaction of phosphonium halide with phenol in a mediumconsisting of aqueous alkaline solution at a temperature of 0 to 55° C.,wherein molar ratio of phenol to phosphonium halide is between 2:1 to10:1 and wherein pH is 9.5 to
 11. 2. The process of claim 1 wherein saidmedium further contains alcohol in an amount of 50 to 200 percentrelative to the weight of the aqueous phase of said solution, saidalcohol having solubility in water of at most 15 percent by weight. 3.The process of claim 1 wherein pH of said aqueous alkaline solution is9.5 to 10.5.
 4. The process of claim 1 wherein pH of said aqueousalkaline solution is 10 to 10.5.
 5. The process of claim 2 whereinamount of alcohol is 66 to 125 wt %.